AbstractOver the years, heavy metal contaminated waste management has been by the use of chemicals where metals are precipitated from the waste. This method of waste management is not financially viable nor environmentally friendly due to the addition of extra chemicals into the environment. In recent times, alternative management practices such phytoremediation and bioremediation are gaining interest. Bioremediation relies on microorganisms to remove toxic elements from the environment. Microorganisms are able to resist the toxicity of heavy metals by either reducing or oxidizing the metals. They utilize heavy metals as an energy source by oxidizing the metals in their periplasm thereby leaving the environment free from heavy metal contamination. Exploring microbial community structure within heavy metal contaminated environment could lead to novel organism for bioremediation application.
This research firstly, investigated samples from Cromwell bottom nature reserve for heavy metals. The Cromwell nature reserve has a complex history of being a dumping site for fly ash which is known to contain heavy metals. We identified eight (8) different heavy metals namely, Chromium (Cr), Cobalt (Co), Nickel (Ni), Copper (Cu), Arsenic (As), Selenium (Se), Cadmium (Cd) and Lead (Pd) at Cromwell nature reserve. As (12.9 mg/kg) and Cu (11.4 mg/kg) metals were the most abundant in terms of concentration. The concentration of arsenic exceeded the acceptable exposure limit of 1mg/kg according to EPA and WHO.
The work further outlined the microbial community structure at Cromwell nature reserve. Two different environmental conditions were factored during the sampling (summer and winter). In both seasons, the dominant phyla across all samples were Proteobacteria, Bacteroidetes, Acidobacteria, Verucomicrobia, Chloroflexi, Actinobacteria and Planctomycetes. The highly dominant phyla were Proteobacteria.
Four subdivisions of the Proteobacteria were seen to be dominant in the Class level. The most abundant was Betaproteobacteria followed by Deltaproteobacteria, Alphaproteobacterial and Gammaproteobacterial. The dominance of Betaproteobacteria could be linked to the anthropogenic activities at Cromwell nature reserve in the past.
At the genus level of classification, most of the bacteria identified at the Cromwell bottom nature reserve are known to possess genes which enables the organisms to thrive in heavy metal contaminated sites either by inherent or acquired tolerance and resistances to the contaminants (Beattie, Henke et al. 2018). The three most dominant organisms from this level of classification were PAC002541, Geobacter and AF467301_g which belonged to the Class Betaproteobacteria. Betaproteobacteria are notable to be associated with environment contaminated with persistent organic pollutant (Zhang, Wang et al. 2010) . Their ability to degrade PAH are well documented.
The results outlined here suggest the possibility of the microbial community at Cromwell acquiring heavy metal reduction or oxidation genes as a survival mechanism against heavy metals identified at the site. Exploring the community structure further could lead to identifying microorganisms for bioremediation application purpose for heavy metal contamination management.
|Date of Award
|3 Nov 2022
|Paul Humphreys (Main Supervisor)